Field of the Invention
The present invention relates to a printed wiring board on which electronic components are mounted.
Description of the Related Art
Conventionally, an electronic component 3 is mounted on pads 7 of a printed wiring board 1 in the following manner. As shown in FIG. 6, the rectangular pads 7 are arranged on the printed wiring board 1, depending on the shape, size, layout, etc., of electrode terminals 5 of the electronic component 3. A solder paste is applied to the pads 7 and the electronic component 3 is placed on the paste. The entire structure is heated by a reflow device. The electronic component 3 is mounted on the pads 7 as the solder paste is melted so that the electrode terminals 5 of the electronic component 3 are soldered to the pads 7 of the printed wiring board 1. In FIG. 6, numerals 2, 4 and 6 designate a mounting area, the body, and wiring, respectively. Japanese Patent Application Laid-Open No. 7-183650 relates to this technique.
The conventional technique shown in FIG. 6 has a problem that a large stress is applied to soldered portions of those pads 7 which are located at the both ends of pad rows during a temperature cycle so that surrounding elements are liable to fail due to rupture of the soldered portions.